The Guanajuato Mining District is a world-class, high-grade, silver-gold, epithermal vein system with low sulfidation and adularia-sericite alteration. It is historically a well-known, studied, and documented mining district.
El Cubo mineralization is typical of the classic high-grade silver-gold, banded epithermal vein deposits with low sulfidation mineralization characterized by adularia-sericite-silica alteration. Silver occurs in dark sulfide-rich bands within the veins with little mineralization but significant alteration minerals in the surrounding wall rocks. Significant silver and gold bearing metallic minerals include argentite or acanthite (Ag 2 S), electrum (native Au/Ag), ruby silver sulfosalt minerals, such as pyrargyrite (Ag 3 SbS 3 ) and polybasite [(Ag/Cu) 6 (Sb,As) 2 S 7 ][Ag 9 CuS 4 ]), naumannite (Ag 2 S), native silver (Ag), native gold (Au), and aguilarite (Ag 4 SeS). Other metallic minerals include pyrite (FeS 2 ), galena (PbS), sphalerite (ZnS), and chalcopyrite (CuFeS 2 ). The silver sulfosalts are commonly found at depth while native silver is generally supergene and found in oxidized areas. As typical of these type systems, galena, sphalerite, and chalcopyrite are found deeper in the vein zones.
The silver rich veins, such as Villalpando, contain quartz, adularia, pyrite, argentite (acanthite), naumannite, and native gold. Gold rich veins, such as San Nicolas, contain quartz, pyrite, minor chalcopyrite and sphalerite, electrum, ........
